Neutral Current Coherent Cross Sections-Implications on Gaseous Spherical TPC's for detecting SN and Earth neutrinos

Abstract

The detection of galactic supernova (SN) neutrinos represents one of the future frontiers of low-energy neutrino physics and astrophysics. The collapse of a neutron star liberates a gravitational binding energy of about 3 × 1053 erg, 99% of which is transferred to neutrinos and antineutrions of all the flavors and only 1% to the kinetic energy of the explosion. In other words, a core-collapse supernova represents one of the most powerful sources of neutrinos and antineutrinos of all flavors in the Universe. The neutron coherence of neutral currents (NC) allows quite large cross sections in the case of neutron rich targets, which can be exploited in detecting earth and sky neutrinos by measuring nuclear recoils. These (NC) cross sections are not dependent on flavor conversions and, thus, their measurement will provide useful information about the neutrino source. In particular they will yield information about the primary neutrino fluxes, i.e. before flavor conversions in neutrino sphere. The advantages of large gaseous low threshold and high resolution time projection counters (TPC) detectors will be discussed. These are especially promising since they are expected to be relatively cheap and easy to maintain. The information thus obtained can also be useful to other flavor sensitive detectors, e.g. the large liquid scintillation detectors like LENA. All together such detectors will provide invaluable information on the astrophysics of core-collapse explosion and on the neutrino mixing parameters. In particular, neutrino flavor transitions in the SN envelope might be sensitive to the value of θ13 and to the unknown neutrino mass hierarchy. Untill a real SN explosion is detected, one can use available earth neutrino sources with similar energy spectra to test the behavior of these detectors. Among them, the ORNL Neutron Spallation source (SNS) and boosted radioactive neutrino beams are good candidates.